Disruption of the thyroid system by diethylstilbestrol and ioxynil in the sea bream (Sparus aurata)
Introduction
Disruption of the endocrine system by xenobiotic compounds is consistently reported in humans and wild life and is a matter of concern worldwide. The effect of xenobiotics on the thyroid system has received relatively little attention, but is now increasingly reported in vertebrates (for review see Boas et al., 2006, Brown et al., 2004, Colborn, 2002, Tan and Zoeller, 2007, Zoeller and Tan, 2007). Thyroid hormones (THs) are crucial for many biological processes (Bentley, 1998, Chan and Kilby, 2000) and thyroid disruption can seriously compromise normal development of exposed species (Boas et al., 2006). In fish a key developmental event is the transition of larvae to juveniles or metamorphosis which is driven by THs and substances interfering with this process may have profound consequences for fitness and survival (Power et al., 2001, Yamano, 2005). A great variety of natural or synthetic chemicals of different classes and sources (e.g., pesticides, industrial by-products or pharmaceutical drugs) are thought to exert an acute effect at different levels of the thyroid cascade. It is consensual that endocrine disrupting chemicals (EDCs) probably act by interfering with TH synthesis, cellular uptake and metabolism, at the level of TH receptors (TRs) and also TH transport by binding to thyroid hormone distributor proteins (THDP) (DeVito et al., 1999, Boas et al., 2006).
The TH transport system in particular may be quite susceptible to EDCs as many chemicals are structurally related to THs and may bind THDPs and disturb homeostasis of extracellular TH levels or even cellular uptake (Divino and Schussler, 1990). In fact many in vitro studies report that TTR, one of the THDPs in vertebrates, has strong affinity for a great number of putative EDCs in human, birds and amphibians (Cheek et al., 1999, Hamers et al., 2006, Ishihara et al., 2003a, Ishihara et al., 2003b, Kudo and Yamauchi, 2005, Meerts et al., 2000, Yamauchi et al., 2003). In fish TTR is an important THDP and binding of EDCs could have a significant effect on normal thyroid status. Recently, in vitro binding assays revealed that a number of chemicals have the ability to bind more strongly than THs to recombinant TTR from the sea bream (sbrTTR) (Morgado et al., 2007a). However, the in vivo effects of EDCs and the consequences of exposure of fish to such compounds are almost completely unexplored. In fact, although the thyroid cascade has been shown to be influenced by environmental chemicals in more than 40 teleost species (Brown et al., 2004) the mechanisms by which they disrupt the thyroid axis are unclear and have never been explored from a TH transport endpoint perspective. In the present study we decided to address this point by testing two compounds, diethylstilbestrol (DES, a synthetic nonsteroidal estrogen) and ioxynil (IOX, a hydroxybenzonitrile herbicide) which in vitro bind strongly to sbrTTR. The experimental design, chemicals and doses utilised were aimed at identifying possible mechanism by which thyroid disruption could occur in vivo and not the dose-related toxic potential of the chemicals at the concentrations normally encountered in the environment. IOX is a widely used herbicide in agriculture and DES was used in the past in medical therapy and they are both recurrently found in the environment. They have a very low water solubility and an octanol/water partition coefficient of log Pow >3 (3.4 for IOX and 5.07 for DES) (Linders et al., 1994, Report Directorate, 2004) which explains their tendency to bioaccumulate. IOX binds sbrTTR and human TTR with very high affinity in vitro (Morgado et al., 2007a, Ogilvie and Ramsden, 1988) and has a toxicity profile in mammals which includes hyperthyroidism and thyroid tumors (rats) (Report Directorate, 2004). Most toxicological studies concerning DES refer to its estrogen-sensitive endpoints and it has a toxicity profile in mammals which includes cancer mainly in estrogen-sensitive organs and tissues and the immune system of mice. Fish test endpoints mainly include survival, growth and reproduction (Daston et al., 1997). DES is thought to direct its toxic action by interaction with estrogen receptors and/or their co-factors (Bains et al., 2007, Baron et al., 2007). However, Ishihara et al., 2003a, Ishihara et al., 2003b reported DES and IOX amongst the strongest binders of serum protein extracts from human, chicken, bullfrog and masu salmon suggesting they have the potential to interfere with the thyroid system (Ishihara et al., 2003b, Morgado et al., 2007a, Yamauchi et al., 2000).
In order to test the hypothesis that the TTR-binders in vitro, DES and IOX, can disrupt the thyroid system in vivo, sea bream were exposed to these two putative EDCs. In parallel, the consequence of exposure to propilthyouracil (PTU) a known anti-thyroid drug was also analysed as a positive control of TH inhibition. A multi-parameter assessment of the thyroid axis was used to identify potential mechanisms of disruption in the sea bream. For this reason, total plasma protein, circulating concentrations of TH and TTR, and TSH, TTR, deiodinases and TRβ transcript abundance were analysed in different tissue. The current study should help establish the mechanisms by which EDCs can affect fish thyroid status. This is important information as in aquatic ecosystems fish are frequently used as sentinels for pollution and the physiological importance of THs means that disruption of this axis may threaten their survival.
Section snippets
Animals and experimental conditions
Maintenance and manipulation of fish in experiments was conducted in accordance with the guidelines of the European Union Council (86/609/EU) and the code of ethics of the World Medical Association for animal experiments.
Juvenile sea bream were obtained from TIMAR (Tavira, Portugal) and maintained in 1000 l open sea water circuits at Ramalhete experimental station (Faro, Portugal) at normal ambient temperature and salinity for the Algarve, Portugal in September. Fish of approximately similar
Condition factor (K)
This parameter is usually used as a comparative and theoretical measure of fish physiological well-being. Values obtained for condition factor of the fish before and after the treatments are represented in Fig. 1A. Data analysis revealed no significant differences between treatment groups and the control (p > 0.05), or between groups at the start and end of the experiment (Student's t-test, p = 0.1). This indicates that fish well-being was not seriously affected by the treatments or by the stress
Discussion
Endocrine disrupting chemicals can affect the thyroid system at different sites and can directly interfere with TH synthesis, TH metabolism and TH-serum transport. They may also bind to TH receptors (TRs) but data to support this hypothesis is still scarce (DeVito et al., 1999) and it has been suggested that TRs may be a less important target for EDCs (Cheek et al., 1999, Ishihara et al., 2003b, Van den Berg, 1990). Should exogenous EDCs interfere with the metabolism of THs by modifying
Conclusion
The results of the study appear to emphasise that the canonical TH-axis regulatory network is not being affected in a conventional way by EDCs since down-regulation of pituitary TRβ does not lead to an increase in TSH mRNA expression. These apparently antagonistic effects are also observed in thyrocytes as PTU seems to increase proliferation of thyroid follicles despite the euthyroid status of treated fish (possibly a response to diminish the active fraction of chemical (Ferreira et al., 2003,
Acknowledgements
We thank Dr. Pedro Guerreiro, Nadia Silva and Bruno Louro for their assistance in the experiments. Work co-financed by POCI 2010 and the European social fund attributed by the Portuguese National Science Foundation (FCT) to project POCTI/CVT/38703/2001, Pluriannual project to CCMAR and a PhD fellowship to IM (SFRH/BD/6091/2001). The funding sources were not directly involved in the research or article preparation.
References (81)
- et al.
Thyroid hormone deiodination in tissues of American plaice Hippoglossoides platessoides: characterization and short-term responses to polychlorinated biphenyls (PCBs) 77 and 126
Comp. Biochem. Physiol. C Toxicol. Pharmacol.
(2000) - et al.
Neuroprotection by estrogen against MPP+-induced dopamine neuron death is mediated by ERα in primary cultures of mouse mesencephalon
Exp. Neurol.
(2007) - et al.
Estrogen receptor-α and the activating Protein-1 complex cooperate during Insulin-like Growth Factor-I-induced transcriptional activation of the pS2/TFF1 gene
J. Biol. Chem.
(2007) - et al.
Dietary accumulation and biochemical responses of juvenile rainbow trout (Oncorhynchus mykiss) to 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126)
Aquat. Toxicol.
(2002) - et al.
Circulating thyroid hormone levels and iodothyronine deiodinase activities in Nile tilapia (Oreochromis niloticus) following dietary exposure to Endosulfan and Aroclor 1254
Comp. Biochem. Physiol. C Toxicol. Pharmacol.
(2005) - et al.
Environmental estrogens and reproductive health: a discussion of the human and environmental data
Reprod. Toxicol.
(1997) - et al.
Stimulation by thyroid hormone analogues of red blood cell Ca2+-ATPase activity in vitro. Correlations between hormone structure and biological activity in a human cell system
J. Biol. Chem.
(1983) - et al.
Membrane receptors mediating thyroid hormone action
Trends Endocrinol. Metab.
(2005) - et al.
Promotion by thyroid hormone of cytoplasm-to-nucleus shuttling of thyroid hormone receptors
Steroids
(2008) - et al.
Receptor-mediated uptake and internalization of transthyretin
J. Biol. Chem.
(1990)
Short-term effects of thyroid hormone in prenatal development and cell differentiation
Steroids
The effect of endocrine disrupting chemicals on thyroid hormone binding to Japanese quail transthyretin and thyroid hormone receptor
Gen. Comp. Endocrinol.
Endocrine disrupting chemicals: interference of thyroid hormone binding to transthyretins and to thyroid hormone receptors
Mol. Cell. Endocrinol.
A unique role of the beta-2 thyroid hormone receptor isoform in negative regulation by thyroid hormone. Mapping of a novel amino-terminal domain important for ligand-independent activation
J. Biol. Chem.
Chronic fasting reduces the response of the thyroid to growth hormone and TSH, and alters the growth hormone-related changes in hepatic 5′-monodeiodinase activity in rainbow trout, Oncorhynchus mykiss
Gen. Comp. Endocrinol.
Thyroid hormones are important for embryonic to larval transitory phase in zebrafish
Differentiation
Temporal expression and T3 induction of thyroid hormone receptors alpha1 and beta1 during early embryonic and larval development in zebrafish Danio rerio
Mol. Cell. Endocrinol.
Protein measurement with the Folin phenol reagent
J. Biol. Chem.
Properties of T4 5′-deiodinating systems in various tissues of the rainbow trout, Oncorhynchus mykiss
Gen. Comp. Endocrinol.
Disruption of thyroid hormone binding to sea bream recombinant transthyretin by ioxinyl and polybrominated diphenyl ethers
Chemosphere
Regulation of transthyretin by thyroid hormones in fish
Gen. Comp. Endocrinol.
Thyroid hormone deiodination in brain, liver, gill, heart and muscle of Atlantic salmon (Salmo salar) during photoperiodically-induced parr-smolt transformation. I. Outer- and inner-ring thyroxine deiodination
Gen. Comp. Endocrinol.
Characterization of a sea bream (Sparus aurata) thyroid hormone receptor-beta clone expressed during embryonic and larval development
Gen. Comp. Endocrinol.
Ioxynil and 3,5,3′-triiodothyronine: comparison of binding to human plasma proteins
Toxicol. Lett.
Cloning of the gene and complete cDNA encoding a type 2 deiodinase from Fundulus heteroclitus
Gen. Comp. Endocrinol.
Kinetic characterization of outer-ring deiodinase activity (ORD) in the liver, gill and retina of the killifish Fundulus heteroclitus
Comp. Biochem. Physiol. B Biochem. Mol. Biol.
Thyroid hormones in growth and development of fish
Comp. Biochem. Physiol., C Toxicol. Pharmacol.
Think globally: act locally. New insights into the local regulation of thyroid hormone availability challenge long accepted dogmas
Mol. Cell. Endocrinol.
Mechanisms that mediate negative regulation of the thyroid-stimulating hormone alpha gene by the thyroid hormone receptor
J. Biol. Chem.
Interaction of chlorinated phenols with thyroxine binding sites of human transthyretin, albumin and thyroid binding globulin
Chem. Biol. Interact.
Hypothyroidism induces type I iodothyronine deiodinase expression in tilapia liver
Gen. Comp. Endocrinol.
Competitive interactions of chlorinated phenol compounds with 3,3′,5-triiodothyronine binding to transthyretin: detection of possible thyroid-disrupting chemicals in environmental waste water
Toxicol. Appl. Pharmacol.
Effect of diethylstilbestrol on thyroid hormone binding to amphibian transthyretins
Gen. Comp. Endocrinol.
Comparative Vertebrate Endocrinology
Cellular and structural biology of the deiodinases
Thyroid
Environmental chemicals and thyroid function
Eur. J. Endocrinol.
Perchlorate affects thyroid function in eastern mosquitofish (Gambusia holbrooki) at environmentally relevant concentrations
Environ. Sci. Technol.
Contaminant effects on the teleost fish thyroid
Environ. Toxicol. Chem.
Thyroid hormone and central nervous system development
J. Endocrinol.
Potential mechanisms of thyroid disruption in humans: interaction of organochlorine compounds with thyroid receptor, transthyretin, and thyroid-binding globulin
Environ. Health Perspect.
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- 1
Present address: Max Planck Research Unit for Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle (Saale), Germany.
- 2
Present address: IMM - Institute for Molecular Medicine, Cell Biology Unit, Lisbon University, Portugal.